1. Field of the Invention
The invention relates to polymeric viscosity index (V.I.) improvers--dispersant additives for petroleum oils, particularly lubricating oils. These additives comprise a copolymer of ethylene with one or more C.sub.3 to C.sub.28 alpha-olefins, preferably propylene, which have been grafted with acid moieties, e.g. maleic anhydride, preferably using a free radical initiator, in a solvent, preferably lubricating oil, and then reacted with a mixture of an acid component, preferably an alkenyl succinic anhydride, and a polyamine having two or more primary amine groups. Or the grafted polymer may be reacted with said acid component prereacted with said polyamine to form salts, amides, imides, etc. and then reacted with said grafted olefin polymer. The invention also relates to processes for preparing the preceding products, their use in oil compositions, and includes an improved solution process for grafting acid moieties, e.g. maleic anhydride, onto the ethylene copolymer by staged, or continuous, addition of maleic anhydride and initiator to thereby carry out the graft reaction in the solution stage permitting a high level of grafting while minimizing side reactions.
2. Prior Disclosures
The concept of derivatizing V.I. improving high molecular weight ethylene copolymers, with acid moieties such as maleic anhydride, followed by reaction with an amine to form a V.I.-dispersant oil additive is known in the art as indicated by the following patents.
U.S. Pat. No. 3,316,177 teaches ethylene copolymers such as ethylene-propylene, or ethylene-propylene-diene, which are heated to elevated temperatures in the presence of oxygen so as to oxidize the polymer and cause its reaction with maleic anhydride which is present during the oxidation. The resulting polymer can then be reacted with alkylene polyamines.
U.S. Pat. No. 3,326,804 teaches reacting ethylene copolymers with oxygen or ozone, to form a hydroperoxidized polymer, which is grafted with maleic anhydride followed by reaction with polyalkylene polyamines.
U.S. Pat. No. 4,089,794 teaches grafting the ethylene copolymer with maleic anhydride using peroxide in a lubricating oil solution, wherein the grafting is preferably carried out under nitrogen, followed by reaction with polyamine.
U.S. Pat. No. 4,137,185 teaches reacting C.sub.1 to C.sub.30 mono carboxylic acid anhydrides, and dicarboxylic anhydrides, such as acetic anhydride, succinic anhydride, etc. with an ethylene copolymer reacted with maleic anhydride and a polyalkylene polyamine to inhibit cross linking and viscosity increase due to further reaction of any primary amine groups which were initially unreacted.
U.S. Pat. No. 4,144,181 is similar to 4,137,185 in that it teaches using a sulfonic acid to inactivate the remaining primary amine groups when a maleic anhydride grafted ethylene-propylene copolymer is reacted with a polyamine.
U.S. Pat. No. 4,169,063 reacts an ethylene copolymer in the absence of oxygen and chlorine at temperatures of 150.degree. to 250.degree. C. with maleic anhydride followed by reaction with polyamine.
A number of prior disclosures teach avoiding the use of polyamine having two primary amine groups to thereby reduce cross-linking problems which become more of a problem as the number of amine moieties added to the polymer molecule is increased in order to increase dispersancy.
German Published Application No. P3025274.5 teaches an ethylene copolymer reacted with maleic anhydride in oil using a long chain alkyl hetero or oxygen containing amine.
U.S. Pat. No. 4,132,661 grafts ethylene copolymer, using peroxide and/or air blowing, with maleic anhyride and then reacts with a primary-tertiary diamine.
U.S. Pat. No. 4,160,739 teaches an ethylene copolymer which is grafted, using a free radical technique, with alternating maleic anhydride and a second polymerizable monomer such as methacrylic acid, which materials are reacted with an amine having a single primary, or a single secondary, amine group.
U.S. Pat. No. 4,171,273 reacts an ethylene copolymer with maleic anhydride in the presence of a free radical initiator and then with mixtures of C.sub.4 to C.sub.12 n-alcohol and amine such as N-aminopropylmorpholine or dimethylamino propyl amine to form a V.I.-dispersantpour depressant additive.
U.S. Pat. No. 4,219,432 teaches maleic anhydride grafted ethylene copolymer reacted with a mixture of an amine having only one primary group together with a second amine having two or more primary groups.
German published application No. 2753569.9 shows an ethylene copolymer reacted with maleic anhydride by a free radical technique and then reacted with an amine having a single primary group.
German published application No. 2845288 grafts maleic anhydride on an ethylene-propylene copolymer by thermal grafting at high temperatures and then reacts with amine having one primary group.
French published application No. 2423530 teaches the thermal reaction of an ethylene copolymer with maleic anhydride at 150.degree. to 210.degree. C. followed by reaction with an amine having one primary or secondary group.
The early patents such as U.S. Pat. Nos. 3,316,177 and 3,326,804 taught the general concept of grafting an ethylene-propylene copolymer with maleic anhydride and then reacting with a polyalkylene polyamine such as polyethylene amines. Subsequently, U.S. Pat. No. 4,089,794 was directed to using an oil solution for free radical peroxide grafting the ethylene copolymer with maleic anhydride and then reacting with the polyamine. This concept had the advantage that by using oil, the entire reaction could be carried out in an oil solution to form an oil concentrate, which is the commercial form in which such additives are sold. This was an advantage over using a volatile solvent for the reactions, which has to be subsequently removed and replaced by oil to form a concentrate. Subsequently, in operating at higher polyamine levels in order to further increase the dispersing effect, increased problems occurred with the unreacted amine groups cross-linking and thereby causing viscosity increase of the oil concentrate during storage and subsequent formation of haze and in some instances gelling. Even though one or more moles of the ethylene polyamine was used per mole of maleic anhydride during imide formation, cross-linking became more of a problem as the nitrogen content of the polymers was increased. One solution was to use the polyamines and then to react the remaining primary amino groups with an acid anhydride, preferably acetic anhydride, of U.S. Pat. No. 4,137,185 or the sulfonic acid of U.S. Pat. No. 4,144,181. The cross-linking problem could also be minimized by avoidance of the ethylene polyamines and instead using amines having one primary group which would react with the maleic anhydride while the other amino groups would be tertiary groups which were substantially unreactive. Patents or published applications showing the use of such primary-tertiary amines noted above are U.S. Pat. No. 4,219,432, wherein a part of the polyamine was replaced with a primary-tertiary amine; U.S. Pat. No. 4,132,661; U.S. Pat. No. 4,160,739; U.S. Pat. No. 4,171,273; German No. P2753569.9; German No. 2,845,288; and French No. 2,423,530.
Still another problem arose when using free radical initiators with mineral oil as the grafting medium is that as the grafting levels were increased to increase the dispersancy level, a larger proportion of the oil molecules in turn became grafted with the maleic anhydride. Then upon subsequent reaction with the amine these grafted oil particles tended to become insoluble and to form haze. To avoid using initiators, such as peroxides, for grafting and to avoid the use of oil, several of the above-noted patents utilized thermal grafting in solvent, preferably while using an ethylene copolymer containing a diene monomer so as to achieve an "ene" type reaction between the unsaturation resulting from the diene moiety and the maleic anhydride. However, generally such "ene" reactions are slower than peroxide grafting.
The present invention represents a further improvement over the art in that it permits the utilization of the generally less expensive polyalkylene polyamines having two primary amine groups, while achieving good dispersancy levels, inhibiting cross-linking and allowing initiator, e.g. peroxide, grafting in oil. The preceding can be obtained by reacting the polymer grafted with the maleic anhydride with an acid component, such as an alkenyl succinic anhydride, together with the polyalkylene polyamine, e.g. polyethyleneamine, or with the reaction product of the acid component and polyalkylene polyamine. In either case cross-linking between ethylene copolymer molecules is reduced or inhibited since many of the polyamine molecules will have one primary group reacted with a maleic anhydride moiety of the ethylene copolymer, while its other primary group is reacted with the acid component. A further advantage is when the grafting is carried out in an oil solution, using a free radical initiator, e.g. a peroxide which is generally much faster with better control, than say depending upon thermal cracking or degradation, oil molecules which become grafted with maleic anhydride and react with the amine, will, to a substantial extent, be solubilized if a long chain acid component is used. Another advantage is that acid component reacted with polyamine which does not become reacted with the grafted ethylene copolymer can be effective per se as a dispersant additive if it has above about 50 carbons, or if it has less than about 50 carbons it may have other properties such as acting as an antirust agent. Thus, long chain acid with more than 50 carbons, usually alkenylsuccinic anhydride, reacted with amine to form oil dispersant additives is well known in U.S. Pat. Nos. 3,154,560; 3,172,892; 3,219,666; etc., while derivatives of acids with less than 50 carbons are taught in U.S. Pat. Nos. 2,466,530; 2,568,876; 2,604,451; 3,004,987; etc.
A further aspect of the present invention is when grafting with a free radical initiator, in solvent or oil, that adding the maleic anhydride and free radical initiator either slowly and continuously over a period of time, or in a series of increments, appears to increase the reaction of the maleic anhydride with the polymer as opposed to undesired side-reactions with oil or solvent molecules. This in turn can permit grafting to higher levels of maleic anhydride without excessive haze.